First Report of Powdery Mildew of Greenhouse Pepper Caused by Leveillula taurica in British Columbia, Canada.

In 2003, powdery mildew of greenhouse pepper (Capsicum annuum L.) was reported simultaneously in two commercial greenhouses at two separate locations near Langley in southern British Columbia. Trace amounts of mildew on the foliage of cv. Zamboni in one operation, and 10 to 80% of the foliage of cv. Triple Four was affected in an organic operation, with losses in fruit yield of 2 to 4 kg/m2, were noted. The greenhouse pepper industry in British Columbia in 2001 comprised 76 ha with sales of $41.3 million (Canadian). Affected areas appeared as a white, powdery coating on the abaxial leaf surface of older foliage while diffuse chlorotic spots were present at corresponding locations on the adaxial surface. In some cases, pale yellow spots appeared on the adaxial portion of the affected foliage during later stages of disease development (2). Hyaline, single-celled pyriform and cylindrical conidia were present in 40:60 proportion, respectively. Both conidia had a network of crests and granules sometimes with tiny thorn-like projections on the surface. These projections were evident also on the lower half of conidiophores. Pyriform conidia ranged in length from 53.8 to 79.5 µm (mean = 68.0, SE = 0.8), and in width from 12.9 to 28.0 µm (mean = 20.1, SE = 0.6, n = 50) with a mean length to width ratio of 3.5. Cylindrical conidia had a length from 48.2 to 84.0 µm (mean = 66.0, SE = 0.9), and in width from 13.4 to 25.2 µm (mean = 18.6, SE = 0.4, n = 50) with a mean length to width ratio of 3.6. Short conidial chains borne on conidiophores consisted of a basal pyriform conidium followed by cylindrical conidium. No cleistothecia were observed. Stomatal penetration and extensive endophytic mycelial growth in the mesophyll layer were evident in foliar tissue cleared with glacial acetic acid/EtOH (1:2) and stained with lactophenol cotton blue. To confirm pathogenicity, a suspension of 2 × 104 conidia/ml from infected pepper leaves was applied onto the abaxial and adaxial leaf surfaces of 60-, 42-, and 28-day-old greenhouse pepper cv. Cubico, tomato cv. Trust, and cucumber cv. Corona, respectively. Plants were maintained in a growth chamber at 25/21°C day/night temperature and 80% relative humidity. Control plants in the same chamber were treated identically but not inoculated. After 21 days, inoculated pepper plants developed foliar powdery mildew symptoms on the abaxial surface, including sporulation similar to that of naturally infected plants. Occurrence of the fungus on the abaxial surface of pepper foliage, presence of endophytic mycelium, and the morphological characteristics of the imperfect state confirm the identity of the fungus (2). To our knowledge, this is the first report of Leveillula taurica (Lév.) G. Arnaud on pepper in British Columbia. The disease was first reported in Ontario, Canada in 1999 (1). References: (1) R. Cerkauskas et al. Plant Dis. 83:781,1999. (2) J. Palti. Bot. Rev. 54:423, 1988.

First Report of Fusarium Stem and Root Rot of Greenhouse Cucumber Caused by Fusarium oxysporum f. sp. radicis-cucumerinum in Ontario.

Fusarium stem and root rot on greenhouse long English cucumber (Cucumis sativus L.) cvs. Bodega and Gardon was observed at four commercial greenhouses in Leamington, Ontario, Canada. Losses of 25 to 35%, representing 2.5 ha, were noted. The greenhouse cucumber industry in Ontario comprises 119 ha, with sales in 1999 of $78 million (Canadian). Some foliar chlorosis developed slowly on the lower foliage of affected plants. Basal stem tissue developed a yellow buff discoloration with superficial rot, followed by advanced stages of stem disintegration, which were accompanied by the production of white buff fungus mycelium and orange spore masses externally, and yellowish or reddish brown discoloration of vascular tissue that extended for 5 to 6 cm. Yellowish brown to brown external discoloration extended throughout the affected roots. In contrast, the main symptoms on cucumber infected by F. oxysporum f. sp. cucurbitaceae are wilt, yellowing, and vascular discoloration. The shape of macroconidia, the presence of microconidia on short lateral phialides, and the occurrence of chlamydospores and sporodochia on acidified potato dextrose agar (aPDA) were used to identify the isolates as F. oxysporum. To confirm pathogenicity and formae specialis designation, the roots of a range of 19-day-old host plants of the family Cucurbitaceae and some of the family Solanaceae were clipped and inoculated with the use of a root-dip method (1), with 5 × 105 spores per ml from 6-day-old aPDA cultures of three isolates and a water check with six plants per isolate. Plants were subsequently grown in a greenhouse soil mix (3:2 Fox sandy loam-peat moss, vol/vol) at 22°C day/19°C night, under environmental conditions similar to those reported elsewhere (1). A 0 (healthy) to 5 (dead) scale was used to rate plants after 30 days. In preliminary studies, cucumber cv. Corona, inoculated with various isolates and grown at 26 to 28°C for 30 days, remained asymptomatic, similar to the results of Vakalounakis 1996 (2) at 30°C and Punja and Parker 2000 (1) at 32°C. Muskmelon (Cucumis melo L. cvs. Early Dawn and Summet), watermelon (Citrullus vulgaris Schrad. cv. Yellow Doll), and cucumber cvs. Tasty Green, Odessa, Mustang, and Orient Express were the most susceptible and had ratings of 3.7, 3.0, 2.3, 3.8, 3.3, 1.1, and 1.6, respectively, with stem and root symptoms similar to those we observed in naturally infected plants and reported previously in other work (1). Cucumber cvs. Calypso, Slicemaster, Flamingo, and Marketmore 76 were less susceptible, with ratings of 0.6, 1.0, 0.1, and 1.0, respectively. No symptoms were observed on tomato (Lycopersicon esculentum Mill. cv. Trust), pepper (Capsicum annuum L. cv. Cubico), or squash (Cucurbita pepo L. cv. Taybelle) in our trials, which is in agreement with other work (1). Symptom development on a range of hosts and the cultural and morphological characteristics of the imperfect state of the fungus in vivo and in vitro confirm the identity of the fungus. To our knowledge, this is the first report of F. oxysporum f. sp. radicis-cucumerinum in Ontario. References: (1) Z. K. Punja and M. Parker. Can. J. Plant Pathol. 22:349, 2000. (2) D. J. Vakalounakis. Plant Dis. 80:313, 1996.

First Report of Powdery Mildew of Greenhouse Pepper Caused by Leveillula taurica in Canada.

In 1999, powdery mildew on cvs. Oberon and Triple 4 of greenhouse pepper (Capsicum annum L.) and cv. FireFlame of chili pepper was reported simultaneously in two commercial greenhouses at two separate locations, Leamington and Vineland, geographically separated by 290 km, in southern Ontario. Losses of 10 to 15% each in the 2 and 3.1 ha greenhouse pepper operations were noted. The greenhouse pepper industry in Canada consists of 89.4 ha with sales of $43.6 million (Canadian). Lesions appeared as a white, powdery coating on the abaxial leaf surface only, generally on the lower foliage of pepper plants, while diffuse chlorotic spots were present at corresponding locations on the adaxial surface. In chili pepper, this chlorosis was restricted to interveinal tissue, causing the leaves to have a somewhat netted appearance. In some cases, pale yellow spots appeared on the adaxial portion of the affected foliage during later stages of disease development. No cleistothecia were observed. Pyriform and cylindrical, hyaline, single-celled conidia were present in equal numbers. Both conidia had a network of crests and granules containing tiny, thornlike projections on the surface. These projections were also evident on the lower half of conidiophores. Pyriform conidia ranged in length from 61.6 to 84.0 µm (mean = 70.8, SE = 0.7) and in width from 14.0 to 25.8 µm (mean = 21.1, SE = 0.4, n = 50), with a mean length to width ratio of 3.4. Cylindrical conidia ranged in length from 54.9 to 80.1 µm (mean = 66.3, SE = 0.9) and in width from 15.7 to 24.1 µm (mean = 18.6, SE = 0.3, n = 50), with a mean length to width ratio of 3.1. Short conidial chains borne on conidiophores consisted of a pyriform conidium first followed by cylindrical conidium. Stomatal penetration and extensive endophytic mycelial growth in the mesophyll layer were evident in foliar tissue cleared with glacial acetic acid:EtOH (1:2) and stained with lactophenol cotton blue. To confirm pathogenicity, conidia from infected pepper leaves were dusted onto the water-misted abaxial leaf surface of 41-day-old greenhouse pepper cvs. Cubico and Edison, and onto the similarly treated adaxial leaf surface of 58-day-old field pepper cv. Renegade. Plants were enclosed in plastic bags for 24 h on a bench. Control plants were treated identically but not inoculated. Inoculated plants developed foliar powdery mildew symptoms, including sporulation similar to that of naturally infected plants. Occurrence of the fungus on the abaxial surface of pepper foliage, presence of endophytic mycelium, and the morphological characteristics of the imperfect state confirm the identity of the fungus. This is the first report of Leveillula taurica (Lév.) G. Arnaud on pepper in Canada. Reference: J. Palti. Bot. Rev. 54:423, 1988.

Occurrence of Turnip Yellow Mosaic Virus on Oriental Cruciferous Vegetables in Southern Ontario, Canada.

Turnip yellow mosaic virus (TYMV) has been reported throughout Europe, New Zealand, and Australia. In 1994, this virus was identified in two field plantings of Bok Choi and one planting of Pak Choi (Brassica campestris Chinensis group var. communis) in Durham and Haldimand-Norfolk counties, respectively. In early October, approximately 25% of the plants were infected at each site. Both the striped flea beetle (Phyllotreta striolata (F.)) and the crucifer flea beetle (P. Cruciferae(Goeze)), reported vectors of the virus (1), were present at each site. Infected plants exhibited bright yellow to yellow-green mosaic mottling and often showed chlorotic lesions on the lower leaves. Vein clearing was also seen on several plants. Plants were often coinfected with turnip mosaic virus. Four symptomatic plants were taken from each field site for testing. Spherical virus particles (28 nm) were identified as TYMV by electron microscopy following post-antibody decoration and enzyme-linked immunosorbent assay with the TYMV Agdia test kit. Symptoms were reproduced on both Bok and Pak Choi by mechanical inoculation into healthy plants. Extended host range susceptibility tests with 14 differential hosts were consistent with those reported in the VIDE database (1). This virus, in the presence of the flea beetle vectors, may pose a threat to susceptible traditional cruciferous vegetables grown extensively in this area. Reference: (1) A. A Brunt et al., eds. Plant Viruses Online: Descriptions and Lists from the VIDE Database. Version: 16th January 1997.

Effect of addition of dried healthy or diseased parsnip root tissue to a modified AIN-76A diet on cell proliferation and histopathology in the liver, oesophagus and forestomach of male Swiss Webster mice.

Umbelliferous crop plants, including the parsnip (Pastinaca sativa L.), elaborate enhanced levels of furocoumarins, including psoralens, when subjected to biotic or abiotic stress. These furocoumarins are recognized to lead to phototoxicity. In this study, the effect of these agents, which are present in diseased parsnip root tissue, on the liver and two tissues on the route of entry to the body (the oesophagus and forestomach) were investigated. Young male Swiss Webster mice were fed for approximately 30 days with modified AIN-76A diets containing 32.5% dried healthy, 32.5% apparently healthy or 32.5% fungicide-treated parsnip root tissue, and 8, 16 or 32.5% dried diseased (Phoma complanata-infected) parsnip root tissue. As controls, three modified AIN-76A diets differing in their edible starch-to-sucrose ratios (C1-C3) were administered for an equal time. Dried healthy parsnip root tissue, compared with controls, did not significantly affect any of the indices of cellular proliferation or histopathological parameters that were assessed. Histopathological examination of the oesophagus and forestomach demonstrated no significant changes as a result of feeding any of the diets containing parsnip tissue. In the liver, the highest level (but neither of the two lower levels) of dried diseased parsnip root tissue led to swelling of the cytoplasm in cells surrounding the central vein of hepatic lobules, with consequent compression of the peripheral cells. Using [3H]thymidine radioautography, a dose-related increase in cell labelling with the level of diseased parsnip root tissue was demonstrated in the liver. Compared with control diet C2 only, the extent of [3H]thymidine labelling in the liver was increased in mice receiving apparently healthy parsnip tissue; a slight, not statistically significant, increase was also noted with fungicide-treated parsnip tissue. Increased [3H]thymidine labelling with the feeding of diseased parsnip tissue was also found in the greater curvature of the forestomach and the region of the oesophageal-forestomach junction, but not at the glandular junction of the forestomach nor in the mid-oesophagus.